In recent years, scientific evidence proving the inadequacy of monolayer cell cultures has triggered the development of techniques allowing culture of cells in a three-dimensional (3D) environment. These techniques include the use of suitable porous biomaterials, i.e. scaffolds, that can be seeded with cells but can also comprise cell clusters, tissue or tissue like structures, biopsies and similar. For example, static in vitro cultures of tumor specimens from epithelial tumors, such as colorectal cancer, have been established, allowing survival and expansion of primary tissue, although to a very limited extent.
As a consequence, tools have been made available to respond to specific needs inherent to these techniques. Among these tools, bioreactors provide a controlled chemo-physical environment suitable for the culturing of cells in 3D. In particular, perfusion bioreactors have proven to be effective in overcoming typical limitations of static cultures. Such limitations include lack of a uniform cell seeding through the scaffold, limited mass transport, i.e. nutrient delivery and waste removal, particularly in a central part of the scaffold.
In this context, WO 2013/182574 A1 presents a 3D perfusion bioreactor and system allowing for a convenient operation and handling within efficient human or animal tissue cell culturing. Beyond others, nutrient availability and oxygen delivery can be increased by using such a 3D perfused bioreactor system.
However, specific cell lines, such as cancer cell lines, being widely used for preclinical studies only marginally reflect the heterogeneity of (tumor) tissue where they derive from. They are mostly genetically homogenous with some limited morphological heterogeneity and adapted to plastic dishes through decades of in vitro cultures. A recent study compared copy-number changes, mutations and mRNA expression profiles of commonly used ovarian cancer cell lines and high-grade serous ovarian cancer tumor samples. Alarmingly, rarely used cell lines in this case resembled more closely the cognate tumor profiles than commonly used cell lines. Because of this, the translation of cell line-based studies to their patient counterparts is not always simple to perform.
The tumor microenvironment consists on cellular, e.g. stromal and immune cells, and non-cellular, e.g. extracellular matrix, components. Even characterized for their malignant invasive cell growth in vivo most cancer cells strongly depend on these factors for sustained growth in vivo as well as in vitro. Stromal and immune cells strongly influence tumor growth patterns.
In the context of colorectal cancer, it has been shown that retaining cell-cell contact increases the efficiency of generating spheroids of tumor cells from primary colorectal cancer specimens. Providing niche-dependent signals can therefore be critical for tumor cells.
On the other hand patient-derived xenograft (PDX) models, generated upon subcutaneous implantation of tumor tissue have been proposed to overcome the limitations of tumor material availability. The efficiency reported depends on the tumor type and for colorectal cancer is about 68%. Tumor growth can be observed after 1-2 months. Studies have shown that the generated tumors are more corresponding to the metastatic lesion than to the primary tumor they were derived from.
For both spheroid cell culture and patient derived xenografts the heterogeneity of the initial tumor microenvironment is lost over time, since only the epithelial cell fraction survives and expands. In the case of the PDX human stromal cells are replaced by mouse stromal cells. The initial composition is therefore drastically changed.
Therefore, there is a need for culture systems or methods allowing survival over time of whole tumor tissue, including involved cell types such as both stromal and epithelial components.